add base for OpenGL map render engine

src/c3nav/mapdata/render/engines/opengl.py

@@ -0,0 +1,61 @@
+import io
+
+import ModernGL
+import numpy as np
+from PIL import Image
+
+from c3nav.mapdata.render.engines.base import RenderEngine
+
+
+class OpenGLEngine(RenderEngine):
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+
+        self.vertices = []
+        self.ctx = ModernGL.create_standalone_context()
+
+        self.color_rbo = self.ctx.renderbuffer((self.width, self.height))
+        self.depth_rbo = self.ctx.depth_renderbuffer((self.width, self.height))
+        self.fbo = self.ctx.framebuffer([self.color_rbo], self.depth_rbo)
+        self.fbo.use()
+
+        self.ctx.clear(*(i/255 for i in self.background_rgb))
+
+        self.prog = self.ctx.program([
+            self.ctx.vertex_shader('''
+                #version 330
+                in vec2 in_vert;
+                in vec3 in_color;
+                out vec3 v_color;
+                void main() {
+                    gl_Position = vec4(in_vert, 0.0, 1.0);
+                    v_color = in_color;
+                }
+            '''),
+            self.ctx.fragment_shader('''
+                #version 330
+                in vec3 v_color;
+                out vec4 f_color;
+                void main() {
+                    f_color = vec4(v_color, 1.0);
+                }
+            '''),
+        ])
+
+    def _add_geometry(self, geometry, fill=None, stroke=None, altitude=None, height=None, shape_cache_key=None):
+        pass
+
+    def get_png(self) -> bytes:
+        if self.vertices:
+            vbo = self.ctx.buffer(np.hstack(self.vertices).tobytes())
+
+            # We control the 'in_vert' and `in_color' variables
+            vao = self.ctx.simple_vertex_array(self.prog, vbo, ['in_vert', 'in_color'])
+            vao.render()
+
+        img = Image.frombytes('RGB', (self.width, self.height), self.fbo.read(components=3))
+
+        f = io.BytesIO()
+        img.save(f, 'PNG')
+        f.seek(0)
+        return f.read()